This invention relates to a process of making crossed-linked dispersions, especially aqueous crossed-linked colorant dispersions.
Aqueous dispersions of pigments are widely used in ink-jet printing. Because a pigment is typically not soluble in an aqueous vehicle, it is often required to use a dispersing agent, such as a polymeric dispersant or a surfactant, to produce a stable dispersion of the pigment in the aqueous vehicle.
Conventional dispersants are adsorbed onto the surface of the particulate solid by physical interactions. Many conventional dispersants suffer from a disadvantage in that they may readily be displaced from the surface of the particulate solid by a more strongly adsorbing or displacing material resulting in destabilization of the dispersion and flocculation.
Various dispersion processes are known. A two-roll milling process of dispersing pigments using polymeric dispersants is disclosed in U.S. Pat. No. 5,310,778. A process where a combination of solvents is used and a polymeric dispersant is precipitated from the solvent mixture onto the finely dispersed pigment particles is disclosed in U.S. Pat. No. 6,923,045.
U.S. Patent Publication No. 20050609977 describes a process for preparing an encapsulated particulate solid dispersed in a liquid medium comprising cross-linking a dispersant with a cross-linking agent having at least two epoxy groups.
JP Laid Open Patent Publication 9-104834 describes a process for producing an aqueous pigment dispersion using a pigment and a resin by first treating the resin with an acidic compound to make the dispersion neutral or acidic, followed by neutralizing the carboxyl group of the resin using a basic compound.
A need exists for an easy-to-operate, more effective, and lower cost process for making stable colorant dispersions. The present invention satisfies this need by providing a process for making a cross-linked colorant dispersion by using a partially neutralized dispersant polymer to effectively adsorb the dispersant polymer onto pigment surface, and reducing the amount of the remaining un-adsorbed polymer so as to reduce or eliminate the interference of un-adsorbed polymer on the cross-linking of the dispersant polymer with a cross-linking agent.